For openSUSE Factory run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:adrianSuSE/openSUSE_Factory/home:adrianSuSE.repo
zypper refresh
zypper install 7zip
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:adrianSuSE/15.6/home:adrianSuSE.repo
zypper refresh
zypper install 7zip
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:adrianSuSE/15.5/home:adrianSuSE.repo
zypper refresh
zypper install 7zip